Structural modelling of fluid ethane with Monte Carlo methods

Recently determined neutron diffraction results for fluid ethane at T = 370 K and four densities were fitted with Reverse Monte Carlo simulations. In addition, Monte Carlo simulations in the NVT-ensemble were performed with a n empirically deduced effective eight-site pair potential. The experimental ly determined total atom pair correlation functions were well reproduced. T he individual atom pair correlation functions calculated with Monte Carlo a nd Reverse Monte Carlo agree very well and show a pronounced fine-structure and a significant density effect. The final configurations were used to ca lculate angular distribution functions that show a disordered arrangement o f the molecules with respect to their centers, but high angle correlations for the nearest neighbour interactions compared to a statistically disorder ed model system. The center-center correlation functions for four special m olecule-pair orientations (crossed, T-shaped, parallel adjacent and paralle l end-to-end) show an increased occurrence of molecular orientations at dis tances that correlate with the minima positions in the corresponding potent ial energy curves for these orientations. The atom pair correlations functi ons for these four special species show that the orientational short range order causes the fine structure in the atom pair correlation functions.